And if it isn't the fuse, then the switch on the brake pedal has come loose. Never heard of the switch failing on the Fiesta, but I suppose it can happen.

Incidentally, I was following a Fiesta the other day and there was only one brake light working on it. When that last bulb fails, the driver may think that there's a bigger problem than merely needing new bulbs!

Luckily, all the bulbs are very easy to change on this model of Fiesta.

I check mine by reversing up to a shop window on a shopping-centre car park and watch 'em in the rear-view mirror.